Add history CSV export

[Jiangzhewen]

Closes #14

Summary

• add a History toolbar export action that opens a CSV export modal
• support selectable from/to dates while keeping dates optional for full export
• fetch history in pages and generate CSV in a Blob Web Worker before downloading
• reuse existing history API and formatting helpers for CSV fields

Validation

• npm ci
• npm run build
• git diff --check
• Playwright local check on /trade/ETH-USD with country mocked to SG: opened History export modal, verified invalid date range validation, and verified the empty-history state for an unconnected wallet

Payout address if accepted: USDC on Arbitrum One: 0xbb29837c5302E242CED1595d7BB8bA3ae7450362

[Jiangzhewen]

Validation note:

• npm ci: passed
• npm run build: passed
• git diff --check: passed
• Playwright local check on /trade/ETH-USD with country mocked to SG: opened the History export modal, verified invalid date range validation, and verified the empty-history state for an unconnected wallet

The Vercel check currently points to why-is-my-account-deployment-blocked, which appears to be the same account-level deployment block affecting other open PRs.

[Jiangzhewen]

Vercel is failing before it reaches the project build with Account is blocked and links to Vercel's account-blocked help page, so this appears to be an account/deployment permission issue rather than a code failure. I re-ran npm run build locally on the current PR head and it completes successfully; the output only contains the existing Rollup/Svelte warnings already present in this project.